Conventionally, a hybrid construction machine in which a part of a drive mechanism is driven by an electric motor is proposed. The construction machine of this type generally includes a hydraulic pump for carrying out a hydraulic pressure drive of a hydraulic pressure work element, such as a boom, an arm, a bucket, etc. A motor generator is connected to an engine for driving the hydraulic pump via a reduction gear. The motor generator operates to assist the engine drive and to generate electricity by using the power generated by the engine, and the obtained electric power is accumulated in a storage battery.
A turning device for turning an upper turning part includes an electric motor in addition to a hydraulic motor as the source of power. The drive of the hydraulic motor is assisted by the electric motor when accelerating the turning device. When decelerating the turning device, the electric motor performs regeneration operation, and the obtained electric power by the regeneration is accumulated in a battery. (For example, see Patent Document 1 below).
There is also a hybrid construction machine which further includes an alternating current motor for driving the work element, such as the turning device, and for driving the hydraulic pump. For example, a turning type construction machine using an electric motor as a source of a turning drive is proposed (see Patent Document 2 below).